In recent years, virtual malls, electronic commerce, and related home pages, such as WWW (World Wide Web) on the Internet, have attracted attention as utilization fields of 3-dimensional CG. Especially, the rapid progress of the Internet provides an environment in which relatively high definition 3-dimensional CG such as games and movies are easily handled at home. In the conventional WWW, a machine called a server, such as a personal computer or a work station, is connected through the Internet to plural machines called clients, such as personal computers. In this system, data such as video, audio, text, window layout, and the like are downloaded from the server in response to a request from a client, and the client reconstructs the downloaded data to obtain necessary information. A communication method based on TCP/IP (Transmission Control Protocol/Internet Protocol) is employed for the server-to-client communication.
In the conventional WWW, data supplied from the server were mainly text data and video data. In recent years, with standardization of VRML (Virtual Reality Modeling Language) and browsers for VRML, there is a movement on foot to transmit 3-dimensional CG itself, such as shape data and texture data constituting a scene.
Hereinafter, the VRML will be briefly described.
In the conventional data format mainly composed of video data and text data, such as HTML (Hyper Text Markup Language), enormous time and cost are required for transmitting video data, especially, animation data. Therefore, in the existing system, network traffic is restricted. On the other hand, in the conventional 3-dimensional CG, all of data including shape data, view data, and luminous data are processed as 3-dimensional data. With the progress of 3-dimensional CG technology, the quality of created image is improved rapidly, and the efficiency is significantly improved with regard to the data quantity when 3-dimensional CG data is transmitted as it is. Usually, the data compression ratio in the case of transmitting 3-dimensional CG data is 1/100 or more as compared with the case of transmitting equivalent image data. Therefore, there is a movement on foot to standardize a method of transmitting 3-dimensional CG data through a network. For example, standardization of 3-dimensional CG data called VRML is proposed (VRML Ver2.0). The VRML Ver2.0 defines shape data called primitive, data formats of luminance data, view data, texture data and the like, and a method of specifying the motion of a rigid body.
Meanwhile, an animation technique for generating an image in real time has attracted attention in the field of 3-dimensional CG. By using the real-time animation technique, real motions of 3-dimensional CG characters are reproduced mainly in CM and movies. For example, a complicated shape such as a human being is represented by a skeletal structure, and the amounts of movement of joints of the skeleton, which change every moment, are defined, whereby the complicated motion can be naturally reproduced.
However, with the conventional 3-dimensional CG modeling languages on the Internet such as the VRML, it is impossible to set the motion in real time to a complicated shape such as a human being. Further, under the existing circumstances, it is impossible to transmit or receive motion data of a 3-dimensional CG character which moves as real as a human being, in real time, through a narrow band network such as a telephone line. In order to solve this problem, for example, Japanese Patent Application No. Hei. 10-203007 discloses a multiple-dimensional stream data transmission and reception apparatus which can transmit and receive motion data of a 3-dimensional CG character in real time.
In this prior art, however, although reproduction of a scene according to the stream data can be performed in real time, a viewer cannot enter the scene interactively to control the generated scene itself. For example, even when the viewer wants to control an object in a virtual space, although the object moves according to the will of the producer of the virtual space (i.e., it moves according to the stream data), the viewer cannot control the object. Further, the prior art cannot meet the viewer's demand to change the object to be controlled.